Chemical vapor deposition (CVD) grown diamonds are moving into the international jewelry market recently. Since the qualities of CVD diamonds are very similar to that of highest-quality natural diamonds, it's difficult to distinguish the CVD diamonds from the natural diamonds. There is thus a growing sense of unease and worry among the customers and diamond dealers, which may lead to serious economic losses. Therefore, various methods for identifying CVD diamonds have been emerged, some widely-used methods are described as follows:
(1) Ultraviolet fluorescence identification method. Some of the natural diamonds emit fluorescence while some do not, but all the CVD diamonds emit special fluorescence. However, the special fluorescence of the CVD diamonds cannot be observed under long-wave ultraviolet light, and only under short-wave ultraviolet light can some weak fluorescence or very weak fluorescence be observed. Therefore, if an inspector has already worked for a long time, it's very likely that he will make a misjudgment.
(2) DiamondView detection method. In this method, a DiamondView monitor is used for identifying diamonds. During the detection, blue-green fluorescence and blue phosphorescence that reflect the specific texture characteristics of a CVD diamond can be observed. However, this method is still not effective to realize a heavy detection work.
(3) Photoluminescence identification method. In this method, a diamond is irradiated with Raman laser, and then an absorption peak at a wavelength of 737 nm can be observed in the stimulated emission spectrum. However, there isn't always an absorption peak in every CVD diamond′ spectrum, the detection result is thus unreliable.
In order to help ensure the fairness and justice of the jewelry market, the inventor of the present application made a lot of experiments on various kinds of natural diamonds, man-made diamonds and optimized diamonds with UV-visible-NIR spectrometer. Surprisingly, the inventor found out that spectral reflectance curve of all the existing colorless or near colorless CVD has a sharp trough at a wavelength of about 230 nm. This is because CVD diamonds are grown in high concentrations of hydrogen under heat treatments, thereby forming C—H bonds. Due to the C—H bonds, the spectral reflectance curve of the CVD diamonds will show an absorption peak at the wavelength of about 230 nm.